The present invention relates to cam-operated timers for appliances.
Many household appliances are equipped with mechanical timers to control their operation. Examples include dishwashers, icemakers, clotheswashers and dryers, wall and outlet timers, microwave ovens, and various other appliances.
While there is thus a diverse variety of applications for timers, most timers have a similar general structure. Typically, the timer includes a wheel or drum outfitted with cam surfaces. Spring metal switch arms are mounted to ride on these cam surfaces to be raised and lowered from the wheel or drum surface in response to the elevation of the cam surfaces.
A timing motor is typically coupled to rotate the cam wheel or drum, such that the switch arms are raised or lowered in accordance with a predefined regular pattern that is defined by the elevation of the cam surfaces on the wheel or drum. In some timers, the timing motor moves the wheel or drum by causing drive pawls to oscillate and move the cam wheel or drum forward in a step-by-step fashion. Such a drive system is referred to as an xe2x80x9cinterval type program drive systemxe2x80x9d. In other timers, the timing motor is connected through a gear train to a toothed surface on the cam wheel or drum to rotate the cam wheel or drum in a continuous manner. Such a drive system is referred to as a xe2x80x9cconstant speed program drive systemxe2x80x9d.
The appliance operator typically sets the timer using a knob that extends outside of the timer housing and can be grasped by the operator. In a typical clotheswasher timer, for example, the operator rotates the knob in a forward direction, thereby rotating the cam wheel or drum in a forward direction, until the cam wheel or drum is an appropriate initial position to begin a timed operation cycle. The user then presses a button, or moves the knob axially to initiate the cycle and also start the timing motor.
Often, it may be necessary to slow the rotation of the cam wheel or drum during operation of the appliance. When such a delay is desirable, timers may be provided having delay mechanisms in order to halt or reduce the speed of the appliance functions being controlled by the timer. There exist various mechanisms for inducing such delay. For instance, some timers include a separate delay wheel that cooperatively functions with the cam wheel. An example of such a timer may be found in U.S. Pat. No. 4,153,824.
U.S. Pat. No. 4,153,824 discloses a rotary control timer for an automatic appliance, such as a washing machine, being driven by an interval type drive system including a saddle pawl connected to an element of the appliance that continuously oscillates or makes other repeated cycles of movement. Prongs on the pawl engage a plurality of peripherally toothed wheels, one of which is connected to the timer cam drum and another of which is free to rotate relative to the cam drum such that one pawl prong continually engages the free rotation wheel while a second pawl prong continually engages the drum connected wheel only intermittently. One tooth on the freely rotatable wheel has a depth approximately three times deeper than the remaining teeth. The actuating pawl has two prongs side by side with the prong associated with the freely rotatable wheel being about three times longer than the prong associated with the fixed wheel. As the longer prong bottoms in each tooth of the freely rotatable wheel, the shorter prong will ride freely above the fixed wheel until the deep tooth on the freely rotatable wheel is reached. At that time both prongs will drop into the teeth of their respective wheels and the pawl will advance both wheels one segment, thus advancing the timer drum connected to the fixed wheel one increment. As a result of this configuration, the timer of U.S. Pat. No. 4,153,824 slows the rotation of the cam drum because the wheel connected to the timer cam will only advance one tooth for each complete rotation of the wheel freely rotatable about the timer shaft.
However, certain drawbacks exist in the timer of the ""824 patent. For example, the rotational period of the timer can be delayed only at one delay speed. It does not provide for delays of varying lengths for the rotation of the cam drum. Further, it does not provide for accelerating the rotation of the cam drum. In many appliances, it would be desirable to have variable speeds of delay or acceleration for certain functions.
In accordance with the principles of the present invention, the drawbacks and difficulties with known cam-operated timers, described above in the background of the invention, are overcome.
In a first embodiment, the present invention features a cam-operated timer having a delay wheel which provides two speeds of a timing delay. In a second embodiment, the timer of the present invention provides for rapid advance of the program cam.
The timer of the present invention includes two drive systems: (1) an interval type delay drive system that is designed to be used with (2) a constant speed program drive system. The interval type delay system drives a delay wheel, and the constant speed program drive system drives the program cam. However, in alternate embodiments of the invention, the interval type delay drive system could also be used with a timer having an interval type program drive system. As mentioned above, the timer of the present invention provides at least two different delay timings. One delay period could be used for a delay to start, where a long delay interval is desired, and the other delay period could be used for an in-cycle delay, where a shorter delay is desired. It will be apparent to those skilled in the art that the delay drive system of the present invention is not limited to two delay periods, but may be adapted for any number of delay periods.
The timer of the present invention includes a rotatable cam carrying member having cam surfaces thereon, and further including a control profile disposed about its periphery including a plurality of teeth and a plurality of plateaus. The timer further includes a rotatable delay wheel having a series of teeth substantially equidistantly spaced one from another, disposed about the periphery of the delay wheel, with at least one of those teeth being of greater depth than the remaining teeth which exhibit a substantially uniform depth. The cam carrying member is fixedly mounted to a shaft. The delay wheel is also located on the shaft, but is freely rotatable about the shaft. The cam carrying member and the delay wheel are rotatably located adjacent one another on the shaft. The timer further includes a constant speed program drive system including a timing motor having a rotor that rotates in response to electrical stimulation and a drive mechanism for causing rotation of the cam carrying member in response to rotation of the rotor. This drive mechanism includes a geartrain having a series of cooperating gears and pinions. Finally, the timer includes a delay pawl which is operatively connected to the drive mechanism. This delay pawl includes first and second prongs spaced such that the first prong cooperates with the cam carrying member and the second prong cooperates with the delay wheel. The first prong is shorter than the second prong.
There are three modes of operation of the timer of the present invention: (1) normal non-delay advancement of the program cam, (2) in-cycle delay advancement, and (3) delay to start timing.
Normal non-delay advancement of the program cam is achieved by the geartrain of the constant speed program drive system. The final output pinion of the drive mechanism engages gear teeth located about the periphery of the program cam in order to advance the program cam. During this mode, the delay pawl is oscillating, but the first prong is riding on a plateau formed by the top radius of the control profile of the program cam, preventing either the first or second prongs of the delay pawl from engaging a rachet tooth on either the cam carrying member or the delay wheel.
As the program cam advances, it rotates into a location requiring in-cycle delay. The delay pawl tip drops off the top radius of the control profile of the cam carrying member during the retraction stroke of the pawl and engages an upper level rachet tooth on the delay wheel. As this occurs, the program cam is advanced into an area having no teeth on the periphery of the program cam to engage with the final output pinion. Thus, the output pinion no longer drives the program cam and the delay wheel is only advanced one tooth by the delay pawl. As the delay pawl continues to oscillate, it will continue advancing the delay wheel one tooth per oscillation. However, since the upper level rachet tooth on the delay wheel will not permit the pawl tip to engage the intermediate level rachet tooth on the program cam, the program cam is not advanced. When the delay pawl drops into either an intermediate tooth or a deep tooth on the delay wheel, it will engage the intermediate tooth on the program cam and advance the program cam one step. When the last step of in-cycle delay is advanced, the program cam is advanced so the gear teeth on its periphery once again engage with the final output pinion and the delay pawl tip is once again lifted onto the top radius of the control profile. At this point, the normal constant speed drive system will take over program cam advancement.
As the program cam advances, it rotates into a location requiring a delay-to-start timing period. The delay pawl drops off the top radius of the control profile of the cam-carrying member during the retraction stroke of the pawl and engages an upper level rachet tooth on the delay wheel. As this occurs, the program cam is advanced into an area having no teeth on the periphery of the cam-carrying member to engage with the final output pinion. Thus, as the delay pawl oscillates forward in the drive stroke, it advances the delay wheel one tooth. As the delay pawl continues to oscillate, it will continue advancing the delay wheel one tooth per oscillation. However, since the upper level rachet tooth on the delay wheel will not permit the paw tip to engage the lower level rachet tooth on the program cam, the program cam is not advanced. An intermediate tooth on the delay wheel will also not permit the pawl tip to engage the lower level rachet tooth on the program cam. When the delay pawl drops into a deep tooth on the delay wheel, it will engage the deep tooth on the program cam and advance the program cam one step. When the last step of delay to start is advanced, the program cam is advanced, the program cam is advanced so that gear teeth on its periphery once again engage the final output pinion and the delay pawl is once again lifted onto a top radius of the control profile. At this point, normal constant speed drive system will take over program cam advancement.
The timer of the present invention also includes a no-back pawl which prevents the cam from being turned backwards when the system is in delay mode. When the constant speed drive pinion is engaged with the gear teeth on the cam, a clutch in the drivetrain of the pinion prevents reverse rotation of the cam. However, in delay mode, the pinion teeth are not engaged with the gear teeth. Thus, the no-back pawl engages with pockets in the back of the cam to prevent reverse rotation of the cam. The no-back pawl is attached to a fixed location in the front housing of the timer.
When used with the constant speed program drive system, an alternate embodiment of the timer of the present invention provides for rapid advance of the cam-carrying member. In this embodiment, the top radius on the control profile is replaced with a top level rachet tooth, permitting the program cam to be advanced at an accelerated rate.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the invention.